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1. Out of the tropics: Macroevolutionary size trends in an old insect order are shaped by temperature and predators

   https://doi.org/10.1111/jbi.14544  

   Svensson, Erik I. ; Gómez‐Llano, Miguel ; Waller, John T. ( December 2022 , Journal of Biogeography)

   Global interspecific body size distributions have been suggested to be shaped by selection pressures arising from biotic and abiotic factors such as temperature, predation and parasitism. Here, we investigated the ecological and evolutionary drivers of global latitudinal size gradients in an old insect order.

   Global.

   Odonata (dragonflies and damselflies).

   We compiled data on interspecific variation in extant and extinct body sizes of Odonata, using an already existing database (The Odonate Phenotypic Database) and fossil data (The Paleobiology Database). We combined such body size data with latitudinal information and data on biotic and abiotic environmental variables across the globe to investigate and quantify interspecific latitudinal size‐gradients (“Bergmann's Rule”) and their environmental determinants. We used phylogenetic comparative methods and a global published phylogeny of Odonata to address these questions.

   Phylogenetic comparative analyses revealed that global size variation of extant Odonata taxa is negatively influenced by both regional avian diversity and temperature, with larger‐bodied species in the suborder Anisoptera (dragonflies) showing a steeper size‐latitude relationship than smaller‐bodied species in the suborder Zygoptera (damselflies). Interestingly, fossil data show that the relationship between wing size and latitude has shifted: latitudinal size trends had initially negative slopes but became shallower or positive following the evolutionary emergence and radiation of birds.

   The changing size‐latitude trends over geological and macroevolutionary time were likely driven by a combination of predation from birds and maybe pterosaurs and high dispersal ability of large dragonflies. Our study reveals that a simple version of Bergmann's Rule based on temperature alone is not sufficient to explain interspecific size‐latitude trends in Odonata. Our results instead suggest that latitudinal size gradients were shaped not only by temperature but also by avian predators, potentially driving the dispersal of large‐sized clades out of the tropics and into the temperate zone.

    

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2. Eye‐body allometry across biphasic ontogeny in anuran amphibians

   https://doi.org/doi.org/10.1007/s10682-021-10102-3  

   Shrimpton, S. J. ; Streicher, J. W. ; Gower, D. J. ; Bell, R. C. ; Fujita, M. K. ; Schott, R. K. ; Thomas, K. N. ( January 2021 , Elements in evolutionary economics)

   Animals with biphasic lifecycles often inhabit different visual environments across ontogeny. Many frogs and toads (Amphibia: Anura) have free-living aquatic larvae (tadpoles) that metamorphose into adults that inhabit a range of aquatic and terrestrial environments. Ecological differences influence eye size across species, but these relationships have not yet been explored across life stages in an ontogenetic allometric context. We examined eye-body size scaling in a species with aquatic larvae and terrestrial adults, the common frog Rana temporaria, using a well-sampled developmental series. We found a shift in ontogenetic allometric trajectory near metamorphosis indicating prioritized growth in tadpole eyes. To explore the effects of different tadpole and adult ecologies on eye-body scaling, we expanded our taxonomic sampling to include developmental series of eleven additional anuran species. Intraspecific eye-body scaling was variable among species, with 8/12 species exhibiting a significant change in allometric slope between tadpoles and adults. Traits categorizing both tadpole ecology (microhabitat, eye position, mouth position) and adult ecology (habitat, activity pattern) across species had significant effects on allometric slopes among tadpoles, but only tadpole eye position had a significant effect among adults. Our study suggests that relative eye growth in the preliminary stages of biphasic anuran ontogenies is somewhat decoupled and may be shaped by both immediate ecological need (i.e. tadpole visual requirements) and what will be advantageous during later adult stages. 

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3. Impact of the acanthocephalan parasite Profilicollis altmani on the fecundity of its crustacean intermediate host, the Pacific mole crab, Emerita analoga

   https://doi.org/10.1111/ivb.12362  

   Bhaduri, Ritindra N. ; Yamaguchi, Taiga J. ; Munguia, Kimberly ; Sandhu, Royal K. ; Coffey, Victoria R. ( January 2022 , Invertebrate Biology)

   Parasites may influence their hosts in multiple ways, ranging from physiological changes and behavioral modifications, to altering life history traits. One fitness component that is often considered in relation to parasitism is host fecundity. The larval acanthocephalan parasite,Profilicollis altmani, commonly infects the Pacific mole crab,Emerita analoga; yet this parasite's effect on the crab's fecundity is unknown. Consequently, we examined the effects of acanthocephalan parasitism on the fecundity of this mole crab species. Crabs were collected from the swash intertidal zone in Monterey Bay, CA, and the following parameters were quantified: crab body size (carapace length) and weight, egg‐bearing status (nongravid and gravid), egg number and diameter, total volume and weight of egg mass, and their developmental stages (from newly laid eggs to recognizable zoea larval stage). Parasite prevalence, intensity of infection, and body size of larval cystacanths (measured as volume) were assessed. Host fecundity was positively correlated with both body size and body weight. No differences in egg weight were found between uninfected and infected crabs. Similarly, no difference in crab body weight at various embryonic developmental phases was documented between uninfected and infected crabs. Cystacanth volumes in infected nongravid and infected gravid crabs were not significantly different. Our study suggests that the parasiteP. altmanidoes not have any appreciable effect on the fecundity ofE. analogaand that female mole crabs undergo normal reproduction and maintain robust population sizes in their natural environments. Our findings thus appear to moderate the pervasive notion of a major impact of parasitism on host reproduction.

    

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4. Post-Diapause DNA Replication during Oogenesis in a Capital-Breeding Copepod

   https://doi.org/10.1093/iob/obad020  

   Monell, K. J. ; Roncalli, V. ; Hopcroft, R. R. ; Hartline, D. K. ; Lenz, P. H. ( June 2023 , Integrative Organismal Biology)

   In high-latitude environments where seasonal changes include periods of harsh conditions, many arthropods enter diapause, a period of dormancy that is hormonally regulated. Diapause is characterized by very low metabolism, resistance to environmental stress, and developmental arrest. It allows an organism to optimize the timing of reproduction by synchronizing offspring growth and development with periods of high food availability. In species that enter dormancy as pre-adults or adults, termination of diapause is marked by the resumption of physiological processes, an increase in metabolic rates and once transitioned into adulthood for females, the initiation of oogenesis. In many cases, individuals start feeding again and newly acquired resources become available to fuel egg production. However, in the subarctic capital-breeding copepod Neocalanus flemingeri, feeding is decoupled from oogenesis. Thus, optimizing reproduction limited by fixed resources such that all eggs are of high quality and fully-provisioned, requires regulation of the number of oocytes. However, it is unknown if and how this copepod limits oocyte formation. In this study, the phase in oocyte production by post-diapause females that involved DNA replication in the ovary and oviducts was examined using incubation in 5-Ethynyl-2′-deoxyuridine (EdU). Both oogonia and oocytes incorporated EdU, with the number of EdU-labeled cells peaking at 72 hours following diapause termination. Cell labeling with EdU remained high for two weeks, decreasing thereafter with no labeling detected by four weeks post diapause, and three to four weeks before spawning of the first clutch of eggs. The results suggest that oogenesis is sequential in N. flemingeri with formation of new oocytes starting within 24 hours of diapause termination and limited to the first few weeks. Lipid consumption during diapause was minimal and relatively modest initially. This early phase in the reproductive program precedes mid-oogenesis and vitellogenesis 2, when oocytes increase in size and accumulate yolk and lipid reserves. By limiting DNA replication to the initial phase, the females effectively separate oocyte production from oocyte provisioning. A sequential oogenesis is unlike the income-breeder strategy of most copepods in which oocytes at all stages of maturation are found concurrently in the reproductive structures.

    

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5. Disentangling the correlated evolution of body size, life history, and ontogeny in miniaturized chelydroid turtles

   https://doi.org/10.1111/ede.12386  

   Cordero, Gerardo A. ( May 2021 , Evolution & Development)

   Organismal miniaturization is defined by a reduction in body size relative to a large ancestor. In vertebrate animals, miniaturization is achieved by suppressing the energetics of growth. However, this might interfere with reproductive strategies in egg‐laying species with limited energy budgets for embryo growth and differentiation. In general, the extent to which miniaturization coincides with alterations in animal development remains obscure. To address the interplay among body size, life history, and ontogeny, miniaturization in chelydroid turtles was examined. The analyses corroborated that miniaturization in the Chelydroidea clade is underlain by a dampening of the ancestral growth trajectory. There were no associated shifts in the early sequence of developmental transformations, though the relative duration of organogenesis was shortened in miniaturized embryos. The size of eggs, hatchlings, and adults was positively correlated within Chelydroidea. A phylogenetically broader exploration revealed an alternative miniaturization mode wherein exceptionally large hatchlings grow minimally and thus attain diminutive adult sizes. Lastly, it is shown that miniaturized Chelydroidea turtles undergo accelerated ossification coupled with a ~10% reduction in shell bones. As in other vertebrates, the effects of miniaturization were not systemic, possibly owing to opposing functional demands and tissue geometric constraints. This underscores the integrated and hierarchical nature of developmental systems.

    

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